Anita Sellstedt in the KBC cafeteriaPhoto: Fredrik Larsson

The aim of our research is to study energy production in microorganisms. The research covers several projects, of which the three main projects will briefly be presented below.

Hydrogen metabolism of Frankia

Nitrogen fixation occurs in Frankia both in free-living as well as in symbioses and may contribute as much as a quarter of the total yearly biologically fixed nitrogen globally in terrestrial ecosystem.

The most important recent achievement in the Frankia research field is the sequencing of three Frankia genomes. We were able to show that there are large differences in the genome sizes. Frankia EANpec1 was found to have the largest genome with 9.0 Mb, while Frankia ACN14a had an intermediate size of 7.5 Mb and Frankia HFPCcI3 was the smallest at 5.4 Mb. These numbers were correlated with geographical origin, host plant distribution and repeated sequences, such as IS. Our findings open up a new era in Frankia research, yielding possibilities to explore the molecular biology of Frankia.

An inevitable source of energy-inefficiency in the nitrogen-fixation process is the evolution of hydrogen; as much as 25% of the in vitro electron-flow through nitrogenase goes to hydrogen evolution. Some nitrogen-fixing systems have dealt with this problem of energy loss through evolving an extra enzyme, called uptake hydrogenase, which is very common in Frankia.

Round vesicles of the bacterium Frankia are shown on the left side and elongated cells of Chalara parvispora on the right side. Left: Light micrograph of the bacterium Frankia showing vesicles; right: Light micrograph of our isolate of Chalara parvispora

Cyanobacteria in association with boreal mosses

We were able to discover that cyanobacteria live in association with feather mosses in the boreal area. We also discovered that they are able of fixing nitrogen and thereby contributing to the N status of that ecosystem.

Heterotrophic production of lipids by algae

Algae are commonly autotrophic carbon dioxide fixing prokaryotes. They are also able of storing different compounds under a variety of conditions. This year a Thesis from my laboratory revealed that some microalgae are able to use glycerol as a carbon source under growing in heterotrophic conditions. Interestingly, a microalgae isolated in the lab and originating from Umeå area has this trait and also accumulated significant amounts of lipids under this condition.

Key Publications

  • Leul M, Normand P, Sellstedt A (2009). The phylogeny of uptake hydrogenases. Int Microbiol. 12(1): 23-28.
  • Normand et al., (2007). Genome structure reflects host biogeography in three plant symbionts Frankia sp. strains. Genome Research, 17, 7-15.
  • Mohapatra A, Leul M, Mattsson U, Sellstedt A (2004). A hydrogen-evolving enzyme is present in Frankia R43. FEMS Microbiol.Lett.236: 235-240
  • DeLuca TH, O Zackrisson, M-C Nilsson, A Sellstedt (2002). Quantifying nitrogen fixation in feather moss carpets. Nature. 419: 917-920.
  • Nzayisenga JC, Eriksson K, Sellstedt A. 2018. Mixotrophic and heterotrophic production of lipids and carbohydrates by a locally isolated microalga using wastewater as growth medium. Bioresource Technology 257: 260-265.